Effective emissivity

A real body at temperature T does not emit with the black body emissive power $\sigma\cdot T^4$ but rather with some fraction $\epsilon$.

The total emittances for a variety of surfaces is given in the following table which is an extract from the slides Radiative heat transfer for the course Heat transfer by John Richard Thome (EPFL, 2008).

Symbol
$\epsilon_{rad}$
Choices
MaterialType / TreatmentTemperaturenomminmaxmedian
AluminiumPolished, 98% pure200-6000.040.060.05
AluminiumCommercial sheet900.09
AluminiumHeavily oxidized90-5400.30.20.330.265
BrassHighly polished2600.04
BrassDull plate40-2600.22
BrassOxidized40-2600.460.560.51
CopperHighly polished electrolyte900.02
CopperSlightly polished to dull400.120.150.135
CopperBlack oxidized400.04
SteelPolished40-2600.070.10.085
Stainless steelafter repeated heating230-9000.50.70.6
PaintBlack gloss400.9
PaintWhite paint400.890.970.93
PaintLacquer400.80.950.875
PaintVarious oil paints400.920.960.94
PaintRed lead900.93